Who else had the incorrect tire diameter and thus incorrect odometer\speedometer\mpg from the factory?

[Darksteel165]

As the title says.

My tire diameter was incorrect from the factory and in turn my speed and milage I accrued was off.
I only found out when I checked the tire size (I am running factory 22s Pirellis on a 2022 Limited at factory 36 psi).
It was set from the factory as 2500mm.
The calculator online for tire diameter shows 285/45R22 as 2560mm
My actual diameter that provides accurate speed is around 2523 (confirmed with GPS speed tracking).

Not only does this affect my speed readout, I accrued less logical miles, but also made my truck even by hand calculations get worse MPG (obviously this doesn't change my actual MPG but doesn't allow me to really know what it is).

I wonder how many other folks have the wrong size set and are seeming getting better OR worse MPG because they had an incorrect measurement\value.

 

[TheLegend]

Well I haven’t actually checked mine to be honest now I’m going to when I get home from work… as much as I want to say I can’t believe it I can. I’d be interested to see this thread and poll results.

 

[Dewey]

Mine is right on. Verified by Waze, a GPS app and my handheld Garmin.

 

[mikeru82]

The speedometer on our 2020 Limited is less than 1 mph off from my gps speed app so I'm assuming the tire size is correct for this truck.

 

[Darksteel165]

Mine is right on. Verified by Waze, a GPS app and my handheld Garmin.

Waze is how I found out mine was wrong.

 

[Jimmy07]

As the title says.

My tire diameter was incorrect from the factory and in turn my speed and milage I accrued was off.
I only found out when I checked the tire size (I am running factory 22s Pirellis on a 2022 Limited at factory 36 psi).
It was set from the factory as 2500mm.
The calculator online for tire diameter shows 285/45R22 as 2560mm
My actual diameter that provides accurate speed is around 2523 (confirmed with GPS speed tracking).

Not only does this affect my speed readout, I accrued less logical miles, but also made my truck even by hand calculations get worse MPG (obviously this doesn't change my actual MPG but doesn't allow me to really know what it is).

I wonder how many other folks have the wrong size set and are seeming getting better OR worse MPG because they had an incorrect measurement\value.

Nobody will ever have 100% accurate speed 100% of the time because the number configured in the BCM is static, while in reality, tire circumference is dynamic. It changes based on tire PSI, weight on the tire, tread depth, and centrifugal force depending on speed.
In your case, you say factory was set to 2500mm (VehConfig 4: Dynamic Tire Circumference), and 2523mm makes it accurate with GPS.
That means the height of the tire from the ground to the center of the hub (the correct way to calculate the radius in order to get the dynamic circumference) is a difference of 9/64” between those two circumferences. That could very well be the difference in height that a few PSI can cause.

 

[Trippi]

Waze is how I found out mine was wrong.

I have no idea how to even check this

 

[Darksteel165]

I have no idea how to even check this

Just use Waze on your phone WITHOUT being connected to Android Auto or Apple Carplay.
It shows your speed.

Nobody will ever have 100% accurate speed 100% of the time because the number configured in the BCM is static, while in reality, tire circumference is dynamic. It changes based on tire PSI, weight on the tire, tread depth, and centrifugal force depending on speed.
In your case, you say factory was set to 2500mm (VehConfig 4: Dynamic Tire Circumference), and 2523mm makes it accurate with GPS.
That means the height of the tire from the ground to the center of the hub (the correct way to calculate the radius in order to get the dynamic circumference) is a difference of 9/64” between those two circumferences. That could very well be the difference in height that a few PSI can cause.

That is all true except I am running factory wheels\tires\psi. It "should" of been right.
It seems it was off by 1-2 mph.
There is also a factory setting that lists "P285/45R22 A/S" which are the tires that came on my Limited which sets it to 2461mm which is even more off so I'm not even sure how they got 2461m.

These are minor things but I just find it very odd.

 

[Jimmy07]

Just use Waze on your phone WITHOUT being connected to Android Auto or Apple Carplay.
It shows your speed.


That is all true except I am running factory wheels\tires\psi. It "should" of been right.
It seems it was off by 1-2 mph.
There is also a factory setting that lists "P285/45R22 A/S" which are the tires that came on my Limited which sets it to 2461mm which is even more off so I'm not even sure how they got 2461m.

These are minor things but I just find it very odd.

If you’re referring to the AlfaOBD list of tires that is not in car configuration change, those are often wrong, and really shouldn’t even bother using them. Those are just tire sizes that the developer compiled on his own, probably mostly calculated off of the “size on paper” that they “should be”. Whatever the case may be, it’s better to just go into car configuration change > VehConfig 4: Dynamic Tire Circumference, and make the change there with the appropriate diameter in mm.

If I was going to compare accurate GPS speed and tire circumference to achieve it at a particular moment in time, vs what the BCM is set to at the factory, I would make sure I had brand new tires same as factory, weight the front and rear axles at a scale, set the tire pressures according to the tire manufacturer load chart, verify that’s where I want to be with the chalk test, then dial in the circumference with gps (divorced from the Uconnect system). That’ll get me a true difference in how far off the factory setting is at that particular moment. But, I have absolutely no idea what the factory’s criteria is for setting that number in the first place is to even argue it, so I think +/- 1 or 2 mph is close enough.

 

[SD Rebel]

Mine was right on, using a GPS program from my cell phone.

I can see how certain trims that offer optional wheels and tire sizes within that trim line could have this issue.

 

[Ftarasi]

I’m running 35” tires on my 2022 1500 eco diesel. My dealer can’t get my speed odometer within 7 mph of what my gps/waze is showing. This is their second try at it, my mpg is way off too.